1. Field of the Invention
The present invention relates to a camera with a built-in electronic flash or strobe which makes flashmatic exposure control even during the daytime so as to provide proper exposure.
2. Description of Related Art
Some types of flashmatic automatic exposure control cameras with program shutters have a feature of flash exposure even in the daytime which is called an ever-flash exposure. One such ever-flash exposure control camera is that described in Japanese Patent Publication No. 57-54777. The approach used is to trigger the electronic flash at a proper timing during opening the shutter so as to provide proper exposure. For the purpose of providing a brief description about the prior art ever-flash exposure that will enhance an understanding of the present invention, reference is made to FIG. 8.
As shown in FIG. 8 showing a time chart of the ever-flash exposure control, a shutter commences to open at a time t.sub.0 and increases linearly the aperture in size or area until a time t.sub.1. After the shutter remains the maximum aperture S.sub.max from the time t.sub.1 to a time t.sub.2, it commences to close quickly and completes the exposure at a time t.sub.3. During gradually increasing the aperture in size of the shutter, the electronic flash is triggered at a proper timing to provide illumination light toward the scene to be photographed. Shifting the flash triggering timing varies an effective quantity of flash illumination light contributory to film exposure (which is hereafter referred to as a contribution ratio of flash illumination light). For instance, the contribution ratio of flash illumination light is the largest when the electronic flash is triggered at times between the times t.sub.1 and t.sub.2. However, the contribution ratio of flash illumination light is reduced according to opened areas of the shutter when the electronic flash is triggered at times before the time t.sub.1.
In the prior art ever-flash exposure control, the flash triggering timing is advanced closely to the time t.sub.0 as the distance of a subject from the camera (which are referred to as a subject distance) becomes short. Due to unstable dynamic operations of the shutter in a short period of time immediately after the commencement of opening, for instance between the time t.sub.0 and a time t.sub.0 +.DELTA.t, the shutter causes unstable dynamic operation. This leads to errors in ever-flash exposure control for subjects at relatively short subject distances in exposure times between the time t.sub.0 and the time t.sub.0 +.DELTA.t. Together, if restricting the flash flush triggering timing after the critical smallest period of time .DELTA.t, there occurs over exposure for close up shots where a subject at a subject distance shorter than a specific subject distance which gives a critical aperture of the shutter, decisive to stable dynamic shutter operation, at the time t.sub.0 +.DELTA.t.